The present invention relates to a vehicle steering system which can perform an automatic steering control and cancel the control.
There are proposed techniques for performing an automatic steering of a vehicle by making use of a steering actuator provided on the vehicle. For example, a power steering system installed on a vehicle includes an electric motor or a hydraulic actuator as a steering actuator for imparting a steering force (a steering assist force) to a steering mechanism. Then, steered road wheels of the vehicle can be turned without involving the manipulation of a steering wheel by the driver by controlling the output of the steering actuator.
More specifically, in an automatic parking assist control, a target traveling path from a current position to a parking position of the vehicle is calculated, and a relationship of a target turning angle with a traveling distance of the vehicle is obtained so that the vehicle is reversed along the target traveling path so calculated. Then, the steering actuator is controlled so as to attain a target turning angle according to a traveling distance of the vehicle. As this occurs, the driver only has to perform the adjustment of stopping position as well as the adjustment of vehicle speed by controlling the brake and accelerator pedals and does not have to manipulate the steering wheel.
In the case that a human being or obstacle such as a moving object other than the human being happens to enter the target traveling path of the vehicle after the vehicle has started reversing, the driver can intervene in the automatic parking control by not only applying the brakes but also imparting a manipulating torque to the steering wheel. As this occurs, it is detected that the manipulating torque imparted to the steering wheel exceeds a predetermined torque threshold value, in response to which the automatic parking control is canceled (see JP-A-2004-284530, for example). In addition to this, the automatic parking control can be canceled according to the intention of the driver by manipulating a predetermined switch which activates the stop of automatic parking control.
When the automatic parking control is performed, there may occur a case where the steering wheel rotates fast depending upon adjustment of the vehicle speed by the driver, an approaching angle to the parking position or a target traveling path. Although there is caused no problem when the rotational speed of the steering wheel is low, in the case that the steering wheel rotating at faster speeds strike the hand or fingers of the driver, the driver may feels uncomfortableness. In particular, during the automatic parking control, the driver adjusts the vehicle speed while looking backwards. When the steering wheel rotating at faster speeds strike the hand or fingers of the driver in such a situation, the driver is astonished by an abrupt impact he or she is given. Although the manipulating torque exceeds the torque threshold value to thereby cancel the automatic parking control when the hand or fingers of the driver are caught by the rotating steering wheel, causing nothing dangerous to the driver, he or she cannot escape from having to sense the feeling of uncomfortableness due to the abrupt impact.
In the related art like this, the intervention in automatic steering control is not always performed properly.